In Figure 1 we show the histograms of the SDSS and WISE magnitudes, magnitude uncertainties, redshifts and
position offsets of these SDSS-WISE quasars. The median value of each
quantity is also indicated in these histograms. The redshift range of these 37842 SDSS-WISE
quasars is from 0.064 to 5.414, with a median value of 1.442, and the \(i\) -band magnitude range is from 14.793 to 21.855, with a median value of 18.883.
All the SDSS \(ugriz\)  magnitudes have been corrected from the Galactic extinction using
a map from [1]}. Throughout the paper the SDSS magnitudes are given in AB magnitudes, while
the WISE magnitudes are given in Vega magnitudes. The significant decreases of quasar numbers
in the histograms of W3- and W4-band magnitude uncertainties are due to the relatively lower
sensitivities of the WISE W3- and W4-band detectors. The median values of uncertainties of WISE W3 and W4 magnitudes are 0.127 and 0.283 respectively, which are
significantly larger than the median values 0.050 and 0.053 in the WISE W1 and W2 bands and the median values (\(<0.043\) ) of the magnitude uncertainties in the SDSS \(ugriz\)  bands.
Although we use 6 arcsec for
the cross-correlation radius between the SDSS and WISE sources, from the position offset distributions
we see that majority of sources actually have offsets smaller than 2 arcsec. Therefore, we are
confident about the reliability of such an SDSS-WISE quasar catalog.
